Development and Integration of Light Water Reactor (LWR) Materials Corrosion Degradation Codes into Grizzly

Engelhardt

Petrov

2022

CMD

A critical review is presented on modeling of the radiolysis of the coolant water in nuclear power reactors with emphasis on ITER. The review is presented in two parts: In Part I, we assess previous work in terms of compliance with important chemical principles and conclude that no model proposed to date is completely satisfactory, in this regard. Thus, some reactions that have been proposed in various radiolysis models are not elementary in nature and can be decomposed into two or more elementary reactions, some of which are already included in the models. These reactions must be removed in formulating a viable model. Furthermore, elementary reactions between species of like charge are also commonly included, but they can be discounted upon the basis of Coulombic repulsion under the prevailing conditions (T < 350 °C) and must also be removed. Likewise, it is concluded that the current state of knowledge with respect to radiolytic yields (i.e., G-values) is also unsatisfactory. More work is required to ensure that the yields used in radiolysis models are truly “primary” yields corresponding to a time scale of nanoseconds or less. This is necessary to ensure that the impact of the reactions that occur outside of the spurs (ionizing particle tracks in the medium) are not counted twice. In Part II, the authors review the use of the radiolysis models coupled with electrochemical models to predict the water chemistry, corrosion potential, crack growth rate in Type 304 SS, and accumulated damage in the coolant circuits of boiling water reactors, pressurized water reactors, and the test fusion reactor, ITER. Based on experience with fission reactors, the emphasis should be placed on the control of the electrochemical corrosion potential because it is the parameter that best describes the state of corrosion in coolant circuits.

Section: Past Radiolysis Modeling Of Fission Reactor Coolant Circuitsmentioning

confidence: 99%

“…These models are now undergoing major refurbishment by inclusion of advanced submodels for calculating the ECP and damage due to stress corrosion cracking. A crack initiation model is also being developed [292].…”

Section: Nomentioning

confidence: 99%

A Critical Review of Radiolysis Issues in Water-Cooled Fission and Fusion Reactors: Part I, Assessment of Radiolysis Models

Engelhardt

Petrov

2022

CMD

“…The first term on the right side of Equation ( 5) arises from the transmission of cations via cation vacancies across the passive film from the metal/barrier layer (m/bl) interface to the barrier layer/solution (bl/s) interface, while the second term reflects the transmission of oxygen ions via oxygen vacancies and/or metal interstitials in the reverse direction. The values of a, b, and c are determined by optimizing the PDM on wide-band, electrochemical impedance spectroscopic (EIS) data measured on the material under the appropriate conditions [14].…”

Section: The Electrochemical Corrosion Potential (Ecp)mentioning

confidence: 99%

“…The parameters in G are defined elsewhere [17] but are readily obtained by optimizing the PDM on EIS data [14]. Substitution of Equation (10) into Equation ( 6) yields:…”

Section: The Electrochemical Corrosion Potential (Ecp)mentioning

confidence: 99%

“…In Part I [1] and in [2], it is shown that the absorption of ionizing radiation (neutrons, γ-photons, and α particles), generates a variety of radiolysis products, including e 2 ) some of them being thermodynamically quite powerful, as measured by the standard reduction potential (Table 1 [3]). Included in this table are data for nitrogen species because nitrogen is formed by the 16 O 8 ( 1 n 0 , 1 p 1 ) 16 N 7 nuclear reaction and from any 14 N 7 (as dissolved N 2 gas) that might be present in the system. Couples having very negative E 0 values are strong reducing species while those having very positive values are strong oxidizing species.…”

Section: Introductionmentioning

confidence: 99%

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A Critical Review of Radiolysis Issues in Water-Cooled Fission and Fusion Reactors: Part II, Prediction of Corrosion Damage in Operating Reactors

Engelhardt

2022

CMD

Self Cite

The radiolysis of water is a significant cause of corrosion damage in the primary heat transport systems (PHTSs) of water-cooled, fission nuclear power reactors (BWRs, PWRs, and CANDUs) and is projected to be a significant factor in the evolution of corrosion damage in future fusion reactors (e.g., the ITER that is currently under development). In Part I of this two-part series, we reviewed the proposed mechanisms for the radiolysis of water and demonstrate that radiolysis leads to the formation of a myriad of oxidizing and reducing species. In this Part II, we review the role that the radiolysis species play in establishing the electrochemical corrosion potential (ECP) and the development of corrosion damage due to intergranular stress corrosion cracking (IGSCC) in reactor PHTSs. We demonstrate, that the radiolytic oxidizing radiolysis products, such as O2, H2O2, HO2−, and OH, when in molar excess over reducing species (H2, H, and O22−), some of which (H2) are preferentially stripped from the coolant upon boiling in a BWR PHTS, for example, renders the coolant in many BWRs oxidizing, thereby shifting the ECP in the positive direction to a value that is more positive than the critical potential (Ecrit = −0.23 Vshe at 288 °C) for IGSCC in sensitized austenitic stainless steel (e.g., Type 304 SS). This has led to many IGSCC incidents in operating BWRs over the past five decades that has exacted a great cost on the plant operators and electricity consumers, alike. In the case of PWRs, the primary circuits are pressurized with hydrogen to give a hydrogen concentration of 10 to 50 cm3/kgH2O (0.89 to 4.46 ppm), such that no sustained boiling occurs, and the hydrogen suppresses the radiolysis of water, thereby inhibiting the formation of oxidizing radiolysis products from water. Thus, the ECP is dominated by the hydrogen electrode reaction (HER), although important deviations from the HER equilibrium potential may occur, particularly at low [H2]. In any event, the ECP is displaced to approximately −0.85 Vshe, which is below the critical potential for IGSCC in sensitized stainless steels but is also more negative than the critical potential for the hydrogen-induced cracking (HIC) of mill-annealed Alloy 600. This has led to extensive cracking of steam generator tubing and other components (e.g., control rod drive tubes, pressurizer components) in PWRs that has also exacted a high cost on operators and power consumers. Although the ITER has yet to operate, the proposed chemistry protocol for the coolant places it close to a BWR operating on Normal Water Chemistry (NWC) without boiling or, if hydrogen is added to the IBED-PHTS, close to a BWR on Hydrogen Water Chemistry (HWC). In the current ITER technology, the concentration of H2 in the IBED-PHTS is specified to be 80 ppb, which is the concentration that will be experienced in both the Plasma Flux Area (PFA) and in the Out of Plasma Flux Area (OPFA). That corresponds to 0.90 cc(STP) H2/KgH2O, compared with 20–50 cc(STP) H2/KgH2O employed in a PWR primary coolant circuit and 5.5 to 22 cc(STP) H2/KgH2O in a BWR on hydrogen water chemistry (HWC). We predict that a hydrogen concentration of 80 ppb is sufficient to reduce the ECP in the OPFA to a level (−0.324 Vshe) that is sufficient to suppress the crack growth rate (CGR) below the practical, maximum level of 10−9 cm/s (0.315 mm/a) at which SCC is considered not to be a problem in a coolant circuit but, in the PFA, the ECP is predicted to be 0.380 Vshe, which gives a calculated standard CGR of 2.7 × 10−6 cm/s. This is more than three orders in magnitude greater that the desired maximum value of 10−9 cm/s. We recommend that the HWC issue in ITER be revisited to develop a protocol that is effective in suppressing both the ECP and the CGR in the PFA to levels that permit the operation of the IBED-PHTS in accordance with the experience gained in fission reactor technology.

The Role of Determinism in the Prediction of Corrosion Damage

2023

CMD

Self Cite

This paper explores the roles of empiricism and determinism in science and concludes that the intellectual exercise that we call “science” is best described as the transition from empiricism (i.e., observation) to determinism, which is the philosophy that the future can be predicted from the past based on the natural laws that are condensations of all previous scientific knowledge. This transition (i.e., “science”) is accomplished by formulating theories to explain the observations and models that are based on those theories to predict new phenomena. Thus, models are the computational arms of theories, and all models must possess a theoretical basis, but not all theories need to predict. The structure of a deterministic model is reviewed, and it is emphasized that all models must contain an input, a model engine, and an output, together with a feedback loop that permits the continual updating of the model parameters and a means of assessing predictions against new observations. This latter feature facilitates the application of the “scientific method” of cyclical prediction/assessment that continues until the model can no longer account for new observations. At that point, the model (and possibly the theory, too) has been “falsified” and must be discarded and a new theory/model constructed. In this regard, it is important to stress that no amount of successful prediction can prove a theory/model to be “correct”, because theories and models are merely the figments of our imagination as developed through imperfect senses and imperfect intellect and, hence, are invariably wrong at some level of detail. Contrariwise, a single failure of a model to predict an observation invalidates (“falsifies”) the theory/model. The impediment to model building is complexity and its impact on model building is discussed. Thus, we employ instruments such as microscopes and telescopes to extend our senses to examining smaller and larger objects, respectively, just as we now employ computers to extend our intellects as reflected in our computational prowess. The process of model building is illustrated with reference to the deterministic Coupled Environment Fracture Model (CEFM) that has proven to be highly successful in predicting crack growth rate in metals and alloys in contact with high-temperature aqueous environments of the type that exist in water-cooled nuclear power reactor primary coolant circuits.